Multiresistance to antibiotics of Salmonella enterica serovar Typhimurium strains producing extended spectrum beta-lactamases (ESBLs).

The purpose of the study is to give the rising incidence of Salmonellosis and the continuous decrease of sensitivity of Salmonella to a range of antibiotics, the prime importance of the choice of optimal anti-infective chemotherapy in order to prevent the selection of multidrug-resistant strains (MDR). We have studied 54 strains of Salmonella sent for further investigation to "Cantacuzino" NIRDMI Bucharest. The statistical analysis was based on the interpretation pathogen susceptibility and analyzed according to CLSI recommendations 2009, which revealed that 8 (14,81%) identified as S. enterica serovar Typhimurium group, presented a phenomenon of MDR. S. Typhimurium strains producing ESBL showed resistance mechanisms associated with beta-lactam resistance to aminoglycosides, quinolones, sulfonamides and tetracyclines.


Introduction
Gastrointestinal infections are caused by gram-negative amounts, ESBL-producing special problems in medical practice, by decreased sensitivity to antibiotics, due to the acquisition of various ways of achieving strength, including the production of ESBL [1]. Given that intestinal infections themselves are a public health problem, etiological involvement of microorganisms resistant to antibiotics increases their severity. A continuous monitorization of the emergence and spread of strains producing extended-spectrum beta-lactamases (ESBLs) is one of the major objectives of health programs that address infectious disease control.

Results and Discussion
Prevalence of Salmonella strains studied is the Enteritis serotypes (51,85%) and Typhimurium (27,78%) -see Table 1. The statistical analysis was based on the interpretation pathogen susceptibility and analyzed according to CLSI, revealing that of the 54 strains of Salmonella tested antibiotically, 8 (14,81%) identified as S. enterica serovar Typhimurium group, presenting the phenomenon of multiresistance to antibiotics (MDR), which meant being resistant to beta-lactams, aminoglycosides, quinolones, tetracycline and sulfonamides. High rates of resistance (>70%) were recorded to ampicillin, cefotaxime, ceftazidime, gentamicin, kanamycin and streptomycin, sulfonamide, trimethoprim, respectively nalidixic acid. The highest level of resistance to tetracycline was obtained (87,5%). Instead, the patient showed 100% sensitivity to cefoxitin, imipenem, and ciprofloxacin. Only 25% of the strains were sensitive to semisynthetic penicillins and cephalosporins (3 rd generation). In addition, a number of 7 strains showed resistance to chloramphenicol (87,5%). The same eight strains were resistant to amoxicillin + clavulanic acid, showing on one hand, the substrate specificity of beta-lactamases and, on the other hand, the possible adaptation of S. Typhimurium in clavulanic acid (a beta-lactamase inhibitor which remains active, the ESBLs, therefore will enhance the action of cephalosporins). According to the method of double diffusion synergy test, antimicrobial test results showed that the 8 strains tested produced beta-lactamase. Strains belonging to this phenotype (ESBLs) were characterized by crossresistance to most beta-lactam tested. All the 8 strains showed ESBLs phenotype associated with phenotypes of resistance to aminoglycosides, cotrimoxazole and tetracycline, and of these, seven showed ESBLs phenotype associated with chloramphenicol resistance phenotype.
This indicative study on the characterization of antibiotic resistance by phenotypic methods strains of S. Typhimurium identified as producing beta-lactamases, showed that all the isolates were resistant to amoxicillin/clavulanic acid and ceftazidime. No strain sensitive to these antibiotics was identified. Carbapenems (imipenem) are beta-lactam antibiotics that were susceptible to all strains of S. Typhimurium producing ESBLs (100% of cases). Similarly, there was no resistant strain of isolated cefamicine (cefoxitim). The most active quinolone antibiotic ciprofloxacin proved that all the 8 strains of S. Typhimurium tested, showed sensitivity. All these antimicrobials may be used as antibiotics of choice in the gastrointestinal infections caused by Salmonella serovar Typhimurium.

Conclusions
Multiresistance to antibiotics of strains producing ESBLs was defined by the presence of concomitant resistance to aminoglycosides, fluoroquinolones and sulfamethoxazole-trimethoprim. S. Typhimurium strains producing ESBL showed resistance mechanisms associated with beta-lactam resistance to aminoglycosides, quinolones, sulfonamides and tetracyclines.
In this context, the increasing prevalence of Salmonella enterica serovar Typhimurium strains resistant to antibiotics and mainly those resistant betalactams, are worrying for the treatment of human salmonellosis.